Subcooling system with thermal storage

ABSTRACT

Embodiments of the present disclosure are directed toward systems and method for cooling a refrigerant flow of a refrigerant circuit with a cool water flow from a cool water storage to generate a warm water flow and to cool the refrigerant flow by a subcooling temperature difference, flowing the warm water flow to the cool water storage, and thermally isolating the warm water flow from the cool water flow in the cool water storage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from and the benefit of U.S.Provisional Application Ser. No. 61/793,632, filed Mar. 15, 2013,entitled “SUBCOOLING SYSTEM WITH THERMAL STORAGE,” which is herebyincorporated by reference.

BACKGROUND

The present disclosure relates generally to cooling systems, and moreparticularly, to subcooling systems for cooling systems.

It has long been recognized that subcooling can improve both efficiencyand capacity of cooling systems (e.g., refrigeration systems).Subcooling systems may include condensers, economizers, flash tanks,heat exchangers, flash intercoolers, and/or compressors (e.g.,multi-stage compressors) for cooling condensed refrigerant liquid beforethe condensed refrigerant liquid reaches the evaporator of a coolingsystem. As the refrigerant is cooled, enthalpy of refrigerant liquidflowing toward the evaporator is reduced, thereby increasing coolingcapacity with little or no change to the work performed by thecompressor. The result is improved cooling system efficiency andcapacity.

SUMMARY

The present invention relates to a system having a refrigerant circuitconfigured to flow a refrigerant and a subcooling circuit configured toflow a cooling fluid. The refrigerant circuit includes a compressor, acondenser, an expansion device configured to expand the refrigerant, asubcooling heat exchanger, and a cooling heat exchanger. The subcoolingcircuit includes the subcooling heat exchanger, a subcooling pump, and athermal storage unit configured to store the cooling fluid.

The present invention also relates to a method that includes cooling arefrigerant flow of a refrigerant circuit with a cool water flow from acool water storage to generate a warm water flow and to cool therefrigerant flow by a subcooling temperature difference, flowing thewarm water flow to the cool water storage, and thermally isolating thewarm water flow from the cool water flow in the cool water storage.

The present invention further relates to a subcooling circuit having athermal storage unit configured to store a cool fluid, a heat exchangerconfigured to transfer heat between a cool fluid flow of the thermalstorage unit and a refrigerant of a cooling system, and a pumpconfigured to pump the cool fluid flow through the subcooling circuit,wherein the thermal storage unit is configured to receive the cool fluidflow from the heat exchanger and to store the cool fluid flow forre-cooling.

DRAWINGS

FIG. 1 is a schematic of a cooling system having a subcooling system, inaccordance with embodiments of the present disclosure;

FIG. 2 is a schematic of a cooling system having a subcooling systemwith thermal storage including a stratified cooling fluid tank, inaccordance with embodiments of the present disclosure;

FIG. 3 is a schematic of a cooling system having a subcooling systemwith thermal storage including a stratified cooling fluid tank, inaccordance with embodiments of the present disclosure;

FIG. 4 is a schematic of a cooling system having a subcooling systemwith thermal storage including multiple cooling fluid tanks, inaccordance with embodiments of the present disclosure;

FIG. 5 is a schematic of a cooling system having a subcooling systemwith thermal storage including a cooling fluid tank with a moveablepartition, in accordance with embodiments of the present disclosure;

FIG. 6 is a schematic side view of a thermal storage tank of asubcooling system, in accordance with embodiments of the presentdisclosure;

FIG. 7 is a schematic top view of a thermal storage tank of a subcoolingsystem, in accordance with embodiments of the present disclosure;

FIG. 8 is a schematic side view of a roller of the thermal storage tankof FIG. 6, in accordance with embodiments of the present disclosure;

FIG. 9 is a schematic of a cooling system having a subcooling systemwith thermal storage including a cooling fluid tank with verticallyarranged fluid connections, in accordance with embodiments of thepresent disclosure;

FIG. 10 is a schematic of a cooling system having a subcooling systemwith thermal storage including multiple cooling fluid tanks arranged inseries, in accordance with embodiments of the present disclosure;

FIG. 11 is a schematic of a cooling system having a subcooling systemwith thermal storage including multiple cooling fluid tanks, inaccordance with embodiments of the present disclosure;

FIG. 12 is a schematic of a cooling system having a subcooling systemwith thermal storage including multiple subterranean fluid storageloops, in accordance with embodiments of the present disclosure;

FIG. 13 is a schematic of a cooling system having a subcooling systemwith thermal storage including a single pass cooling fluid system, inaccordance with embodiments of the present disclosure;

FIG. 14 is a schematic of a cooling system having a subcooling systemwith thermal storage including multiple coolers and subcoolers arrangedin parallel, in accordance with embodiments of the present disclosure;

FIG. 15 is a schematic of a cooling system having a subcooling systemwith thermal storage including two vertically arranged cooling fluidtanks, in accordance with embodiments of the present disclosure;

FIG. 16 is a pressure-enthalpy diagram for the cooling system of FIG.15, in accordance with embodiments of the present disclosure;

FIG. 17 is a schematic of a cooling system having a subcooling systemwith thermal storage including an ice storage tank, in accordance withembodiments of the present disclosure; and

FIG. 18 is a schematic of a cooling system having a subcooling systemwith thermal storage tanks coupled in series, in accordance withembodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed towards improvedsubcooling systems for cooling systems (e.g., refrigeration systems). Aswill be appreciated, subcooling increases cooling capacity of a coolingsystem by reducing the enthalpy of refrigerant entering an evaporator(e.g., cooler) of the cooling system. For example, energy removed fromthe refrigerant liquid may correspond to an increase in cooling capacityof the cooling system. As described in detail below, the disclosedembodiments may include a cooling system with subcooling system having asubcooling heat exchanger that uses a cooling fluid (e.g., water, glycolsolution, carbon dioxide, refrigerant) flow to absorb heat from arefrigerant flow of the cooling system. In particular, a flow rate ofthe cooling fluid flow through the heat exchanger may be regulated tomaximize the efficiency of the subcooling system. For example, thecooling fluid flow rate may be adjusted such that a temperature changeof the cooling fluid flow across the subcooling heat exchanger may besimilar or equal to a temperature change of the refrigerant across thesubcooling heat exchanger. Furthermore, in certain embodiments, thesubcooling system may include a thermal storage unit, such as a coolingfluid tank, which may be a rechargeable source of the cooling fluidflow.

Turning now to the drawings, FIG. 1 is a schematic of a cooling system10 having an improved subcooling system 12 in accordance with presentembodiments. The cooling system 10 may be any suitable cooling systemthat supplies a chilled fluid to a load 14 and/or chills a fluid flowsupplied to the load 14. For example, the cooling system 10 may be achiller, a room air conditioner, a residential split-system airconditioner, or other type of refrigeration system. As described indetail below, the cooling system 10 may include a refrigerant circuitthat chills a fluid flow supplied to the load 14. Additionally, thesubcooling system 12 may be configured to further cool the refrigerantflowing through the refrigerant circuit of the cooling system 10 with asubcooling fluid flow, thereby increasing the capacity of therefrigerant to absorb heat. For example, in certain embodiments, thesubcooling system 12 may cool the refrigerant between a condenser and anexpansion valve of the refrigerant circuit. As may be appreciated, thecondenser and the expansion valve reduce the temperature and theenthalpy of the refrigerant. As described herein, the subcooling system12 may further cool and decrease the enthalpy of the refrigerant. Theadditional temperature and enthalpy reduction from the subcooling system12 may increase the capacity of the cooling system for a particularamount of work, such as the work of a compressor of the cooling system10. For example, the subcooling system 12 may increase the capacity ofthe cooling system from approximately 7,000 kW with 2,500 kW input powerto approximately 9,000 kW with 2,500 kW input power. Additionally, or inthe alternative, the additional temperature and enthalpy reduction fromthe subcooling system 12 may reduce the amount of work (e.g., from 3,500kW to 2,500 kW) to provide a particular amount (e.g., 9,000 kW) ofcooling. Furthermore, as discussed below, the subcooling system 12 mayinclude a thermal storage unit, such as a cooling water tank, which maybe rechargeable. In this manner, efficiency of the subcooling system 12and the cooling system 10 may be improved.

FIG. 2 is a schematic of an embodiment of the cooling system 10 having arefrigerant circuit 20 and the subcooling system 12. For example, thecooling system 10 may be a water-cooled or air-cooled chiller. As shown,the cooling system 10 includes the refrigerant circuit 20 configured tocool a load fluid 22, which includes fluid passing through a loadcircuit 23 portion of the cooling system 10. The load fluid 22 mayinclude, but is not limited to, water, deionized water, glycol solution,carbon dioxide, a refrigerant (e.g., R134a, R410A, R32, R1233ZD(E),R1233zd (E), R1234yf, R1234ze), or any combination thereof. Morespecifically, the refrigerant circuit 20 includes a cooler 24 in which arefrigerant 25 may cool the load fluid 22. The cooler 24 may also bereferred to herein as a cooling heat exchanger. The refrigerant 25 mayinclude, but is not limited to, carbon dioxide, R134a, R410A, R32,R1233ZD(E), R1233zd (E), R1234yf, or R1234ze, or another refrigerant asmay be appreciated by one of skill in the art. The refrigerant circuit20 further includes a compressor 26 (e.g., centrifugal compressor, screwcompressor, scroll compressor, reciprocating compressor, or linearcompressor), a condenser 28, and an expansion device 30 (e.g., a fixedorifice, an electronic expansion valve, a motorized butterfly valve, ora thermal expansion valve).

The subcooling system 12 is thermally coupled to the refrigerant circuit20 to subcool the refrigerant 25. For example, the subcooling system 12may be coupled to the refrigerant circuit 20 via a subcooling heatexchanger 32 disposed along the refrigerant circuit 20 between thecondenser 28 and the expansion device 30 (e.g., expansion valve). Assuch, the subcooling system 12 may flow a cooling fluid 33 (e.g., coolwater) through a subcooling circuit 34 and through the subcooling heatexchanger 32. In some embodiments, the cooling fluid 33 may besubstantially the same fluid as the load fluid 22. Indeed, with respectto the embodiments of FIG. 2, different names for the load fluid 22 andcooling fluid 33 are utilized to facilitate communication of uses of thefluid within the cooling system 10. Additionally, or in the alternative,the cooling fluid may include, but is not limited to, water, deionizedwater, glycol solution, carbon dioxide, a refrigerant (e.g., R134a,R410A, R32, R1233ZD(E), R1233zd (E), R1234yf, R1234ze), or anycombination thereof. In this manner, heat may be transferred from therefrigerant 25 of the refrigerant circuit 20 to the cooling fluid 33(e.g., cool water) of the subcooling circuit 34 via the subcooling heatexchanger 32. Additionally, a thermal storage unit 36 is disposed alongthe subcooling circuit 34 of the subcooling system 12. For example, thethermal storage unit 36 may be a stratified water tank configured tostore the cooling fluid 33 flowing through the subcooling system 12. Thesubcooling system 12 further includes a plurality of valves (e.g., afirst valve 38 between the load 14 and the chilled fluid pump 48, asecond valve 40 between the thermal storage unit 36 and the chilledfluid pump 48, a third valve 42 between the cooler 24 (e.g., coolingheat exchanger) and the thermal storage unit 36, and a fourth valve 44between the subcooling heat exchanger 32 and the thermal storage unit36), which may be operated to regulate the cooling fluid 33 flowingthrough the subcooling circuit 34. As the flow of the cooling fluid 33is regulated by the valves 38, 40, 42, and 44, heat transfer between thecooling fluid 33 of the subcooling system 12 and the refrigerant 25 ofthe cooling system 10 may be regulated. In certain embodiments, thesubcooling system 12 may have different modes of operation based onwhich of the valves 38, 40, 42, and 44 are opened, and which of thevalves 38, 40, 42, and 44 are closed.

For example, when the first valve 38 is configured to allow the loadfluid 22 to flow from the load 14 to the chilled fluid pump 48, thethird valve 42 is closed, and the second valve 40 and the fourth valve44 are open, the subcooling system 12 may be in a subcooling mode. Inthe subcooling mode, at least a portion (e.g., approximately 5 to 20percent) of the load fluid 22 (e.g., return water 45, cold chilled fluid33) may flow from the chilled fluid pump 48 through the subcooling heatexchanger 32, as indicated by arrow 46, to a top 47 of the thermalstorage unit 36 (e.g., stratified water tank). The remainder of the loadfluid 22 from the chilled fluid pump 48 may flow through the cooler 24(e.g., cooling heat exchanger). As will be appreciated, within thethermal storage unit 36, a temperature gradient may exist across thecooling fluid 33 within the thermal storage unit 36. More specifically,the temperature of the cooling fluid 33 (e.g., water) at a bottom 49 ofthe thermal storage unit 36 may be lower than the temperature of thecooling fluid 33 at the top 47 of the thermal storage unit 36. As such,cold cooling fluid 33 from the bottom 49 of the thermal storage unit 36may flow into and join the return water 45 flow upstream of the chilledfluid pump 48. The addition of the cold cooling fluid 33 from thethermal storage unit 36 enables the cooling fluid 33 through thesubcooling heat exchanger 32 to be at a lower temperature than thereturn water 45.

As mentioned above, the flow rate of the cooling fluid 33 (e.g., returnwater 45 and cold cooling fluid 33 from the thermal storage unit 36)flowing through the subcooling circuit 34 may be regulated to achieve adesired temperature drop of the refrigerant 25 across the subcoolingheat exchanger 32. More specifically, the valves 38, 40, 42, and 44 maybe regulated such that a temperature difference (e.g., increase) of thecooling fluid 33 across the subcooling heat exchanger 32 isapproximately equal to the temperature difference (e.g., decrease) ofthe refrigerant 25 across the subcooling heat exchanger 32. The resultis that the temperature of the refrigerant 25 (e.g., liquid refrigerant)may approach the temperature (e.g., between approximately 32 to 50° F.)of the cooling fluid 33 entering the subcooling heat exchanger 32, andthe temperature of the cooling fluid 33 may approach the temperature(e.g., approximately 60, 80, 100, 120, 140° F.) of the refrigerant 25leaving the condenser 28. The expansion device 30 receiving therefrigerant 25 downstream of the subcooling heat exchanger 32 reducesthe pressure and the temperature of the refrigerant 25, thereby enablingthe refrigerant 25 to cool the load fluid 22 via the cooler 24 (e.g.,cooling heat exchanger). For example, the change (e.g., increase) intemperature of the cooling fluid 33 may be approximately 40 to 80° F.across the subcooling heat exchanger 32, and the change (e.g., decrease)in temperature of the refrigerant 25 may be approximately 40 to 80° F.across the subcooling heat exchanger 32. As a result, the energy storagecapacity of the thermal storage unit 36 may be much greater than that ofconventional chilled water storage systems.

In some embodiments, the flows of the refrigerant 25 and the coolingfluid 33 through the subcooling heat exchanger 32 may approximate acounterflow configuration. For example, multi-pass brazed-plate heatexchangers, such as those available by SWEP of Landskrona, Sweden, maybe utilized. Multi-pass brazed-plate may have a substantially compactprofile and/or footprint, and may efficiently transfer heat betweenfluids. In some embodiments, the temperature difference between therefrigerant 25 exiting the subcooling heat exchanger 32 and the coolingfluid 33 entering the subcooling heat exchanger 32 may be less thanapproximately 10, 8, 5, or 2 degrees Fahrenheit. In some embodiments,the temperature difference may correspond to an effectiveness of thesubcooling heat exchanger greater than approximately 90, 91, 92, 93, 94,or 95 percent. The flow rate of the cooling fluid 33 through thesubcooling heat exchanger 32 relative to the flow rate of therefrigerant 25 may be adjustable, thereby enabling the control of thetemperature difference between the exiting refrigerant 25 and theentering cooling fluid 33. In some embodiments, the relative flow rateof the cooling fluid 33 may be adjusted based on a desired coolingcapacity of the cooling system 10, a thermal storage capacity of thethermal storage unit 36, or any combination thereof. For example, therelative flow rate of the cooling fluid 33 may be decreased, therebyreducing the temperature difference between the exiting refrigerant 25and the entering cooling fluid 33, to increase the cooling capacity ofthe cooling system. Alternatively, the relative flow rate of the coolingfluid 33 may be increased, thereby increasing the temperature differencebetween the exiting refrigerant 25 and the entering cooling fluid 33, todecrease the thermal energy transferred from the thermal storage unit 36to the refrigerant 25.

In some embodiments, the subcooling system 12 may be at least partiallydisposed in an environment subject to temperatures near or belowfreezing (e.g., 32° F.). The subcooling system 12 may include thermalinsulation about portions of the subcooling circuit 34, heaters (e.g.,gas heaters, electric heaters), or any combination thereof. Additionallyor in the alternative, the cooling fluid 33 of the subcooling system 12may be mixed with propylene, ethylene glycol, or an antifreeze, therebylowering the freezing point of the cooling fluid 33 below an expectedfreezing environment temperature. In some embodiments, a valve 51 (e.g.,solenoid valve) in the refrigerant circuit 20 disposed between thecondenser 28 and the subcooling heat exchanger 32 may close to prevent athermosiphon when the refrigerant circuit 20 is not circulating therefrigerant 25.

To achieve the desired temperature gradients across the subcooling heatexchanger 32, the cooling system 10 may include one or more sensors 50on the refrigerant circuit 20 and/or the subcooling system 12. Each ofthe one or more sensors 50 is configured to measure one or moreoperating parameters (e.g., temperature, pressure, etc.) of therefrigerant 25 and/or the cooling fluid 33. The sensors 50 may providemeasured feedback to a controller 52 (e.g., an automation controller,programmable logic controller, distributed control system, etc.) by awireless (e.g., via an antenna 53) or hard wired connection. In certainembodiments, the controller 52 may be further configured to regulate(e.g., automatically) operation of one or more of the valves 38, 40, 42,and 44 in response to feedback measured by the sensors 50. In otherembodiments, the valves 38, 40, 42, and 44 may be operated manually.Additionally, other processes of the cooling system 10 may be controlledby the controller 52 by a wireless (e.g., via the antenna 53) or hardwired connection.

In a recharge mode of the subcooling system 12, the second and fourthvalves 40 and 44 are closed, while the first valve 38 and third valve 42are opened to allow the flow indicated by arrows 54. As a result, duringoperation in the recharge mode, the cooling fluid 33 (e.g., water) flowsthrough the subcooling circuit 34, as indicated by arrows 54. Morespecifically, warm cooling fluid 33 from the top 47 of the thermalstorage unit 36 flows through the cooling system 10, causing the coolingfluid 33 to decrease in temperature. Thereafter, the cooling fluid 33 isreturned to the bottom 49 of the thermal storage unit 36. As a result,the cooling fluid 33 within the thermal storage unit 36 may graduallydecrease in temperature, thereby “recharging” the thermal storage unit36.

Flow rate of the cooling fluid 33 (e.g., water) through the thermalstorage unit (e.g., tank) 36 may be much higher during recharge modethan during subcooling mode. As shown in FIG. 2, the full flow of thechilled fluid pump 48 would be directed through the thermal storage unit36 during recharge mode when the fourth valve 44 is closed, while only asmall fraction of the flow (between approximately 5 to 20 percent) wouldbe directed through the thermal storage unit 36 (e.g., through thesecond valve 40) in subcooling mode when the fourth valve 44 is open.This difference in flow rates between the recharge mode and thesubcooling mode means that stratified conditions within the thermalstorage unit 36 (e.g., stratified water tank) are relatively easy tomaintain in subcooling mode, but mixing may occur during recharge.

In certain embodiments, the thermal storage unit 36 (e.g., stratifiedwater tank) may include piping configured to minimize mixing of coolingfluid 33 entering the thermal storage unit 36. For example, the diameterof the piping, the arrangement of the piping into the thermal storageunit 36, and a flow rate of the cooling fluid 33 through the piping mayreduce mixing of the cooling fluid within the thermal storage unit 36,thereby enabling stratification of the cooling fluid 33. As may beappreciated, the density of the cooling fluid 33 is based at least inpart on the temperature of the cooling fluid 33. For example, thedensity of water generally decreases as the temperature increases.Accordingly, a relatively large difference (e.g., greater than 10, 20,30, 40, or 50° F.) in temperature between the cold cooling fluid 33 inthe thermal storage unit 36 and the warm cooling fluid 33 returning fromthe subcooling heat exchanger 32 may enable the warm cooling fluid toreadily stratify above the cold cooling fluid. In other embodiments, thethermal storage unit 36 may include piping to mix entering cooling fluid33 (e.g., warm water) with cooling fluid 33 (e.g., cold water) at thebottom 49 of the thermal storage unit 36. Furthermore, in certainenvironments, the thermal storage unit 36 may be designed to have wallsto withstand elevated environmental pressures. It may be desirable forthe exterior of the thermal storage unit 36 to include thermalinsulation to reduce heat transfer to the environment. The insulationmay be placed on the inside or the outside of the walls of the thermalstorage unit 36.

FIG. 3 is a schematic of an embodiment of the cooling system 10 havingthe refrigerant circuit 20 and the subcooling system 12. Specifically,the illustrated embodiment of the cooling system 10 allows for apressure difference between the thermal storage unit 36 of thesubcooling system 12 and the refrigerant circuit 20. Additionally, theillustrated embodiment has similar elements and element numbers as theembodiment shown in FIG. 2.

As similarly described above, the cooling system 10 has the first,second, third, and fourth valves 38, 40, 42, and 44 to control the flowof the load fluid 22 and the cooling fluid 33 through the cooler 24(e.g., cooling heat exchanger) and subcooling heat exchanger 32. Forexample, the first, second, third, and fourth valves 38, 40, 42, and 44may be low-leakage valves, such as ball valves. The first valve 38 isbetween the cooler 24 (e.g., cooling heat exchanger) and the load 14,the second valve 40 is between the cooler 24 (e.g., cooling heatexchanger) and the thermal storage unit 36, the third valve 42 isbetween the thermal storage unit 36 and the chilled fluid pump 48, andthe fourth valve is between the load 14 and the chilled fluid pump 48.Moreover, in addition to the chilled fluid pump 48, the illustratedembodiment includes a subcooling pump 100 configured to pump the coolingfluid 33 through the subcooling circuit 34, which may be at a differentpressure than the load fluid 22 fluidly coupled to the load 14. Thefirst, second, third, and fourth valves 38, 40, 42, and 44 and the pumps48 and 100 may be regulated or controlled (e.g., via a control systemincluding the automation controller 52) to enable operation of thecooling system 10 and subcooling system 12 in different modes.

For example, the first and second valves 38 and 40 control flow of thechilled fluid (e.g., load fluid 22, cooling fluid 33) leaving the cooler24 (e.g., cooling heat exchanger). Specifically, the first valve 38controls the flow of chilled load fluid 22 to the load 14 (e.g., abuilding chilled water loop) during the subcooling mode. Additionally,the second valve 40 controls the flow of chilled cooling fluid 33 fromthe cooler 24 (e.g., cooling heat exchanger) to the bottom 49 of thethermal storage unit 36 (e.g., stratified water tank) during therecharge mode. As further shown, the third and fourth valves 42 and 44are disposed on the suction side of the chilled fluid pump 48.Specifically, the third valve 42 regulates flow of the cooling fluid 33from the top 47 of the thermal storage unit 36 to the chilled fluid pump48 during the recharge mode, and the fourth valve 44 controls flow ofthe load fluid 22 (e.g., return water 45) returning from the load 14 tothe chilled fluid pump 48 during the subcooling mode.

Furthermore, the subcooling pump 100 draws the cooling fluid 33 from thebottom 49 of the thermal storage unit 36 and pumps the cooling fluid 33from the thermal storage unit 36 through the subcooling heat exchanger32 to subcool the refrigerant 25 of the refrigerant circuit 20. Afterpassing through the subcooling heat exchanger 32, the cooling fluid 33flows to the top 47 of the thermal storage unit 36. As described above,the cooling fluid 33 flowing through the subcooling heat exchanger 32absorbs heat from the refrigerant 25 flowing through the refrigerantcircuit 20 of the cooling system 10 via the subcooling heat exchanger 32(e.g., subcooler). In certain embodiments, the flow rate of coolingfluid 33 through the subcooling pump 100 and subcooling heat exchanger32 may be much lower than the flow rate of fluid (e.g., load fluid 22,cooling fluid 33) through the chilled fluid pump 48. For example, thechilled fluid pump 48 may pump a fluid (e.g., load fluid 22, coolingfluid 33) at approximately 10 to 20 times the rate that the subcoolingpump 100 pumps the cooling fluid 33. In some embodiments, the subcoolingpump 100 may pump the chilled fluid 33 at a flow rate that enables thetemperature of the cooling fluid 33 exiting the subcooling heatexchanger 32 to be less than 5, 4, 3, 2, or 1° Fahrenheit of thetemperature of the refrigerant 25 entering the subcooling heat exchanger32. The subcooling pump 100 may be a variable speed circulator pump, asmay be available by Taco of Cranston, R.I. As may be appreciated,decreasing the temperature difference between the exiting cooling fluid33 and the entering refrigerant 25 via control of the subcooling pump100 may increase the efficiency of the cooling system 10. Moreover, insome embodiments, the subcooling pump 100 may pump the chilled fluid 33through the subcooling heat exchanger 32 at a flow rate less than theflow rate of the refrigerant 25 through the subcooling heat exchanger32. For example, the flow of the chilled fluid 33 through the subcoolingheat exchanger 32 may be approximately 5, 10, 20, 30, 40, 50 of the flowrate of the refrigerant 25 through the subcooling heat exchanger 32. Theflow rate of the chilled fluid 33 through the subcooling heat exchanger32 relative to the flow rate of the refrigerant 25 through thesubcooling heat exchanger 32 may be variable, based at least in part ona desired cooling capacity of the cooling system.

During a subcooling mode of the illustrated embodiment in FIG. 3, thechilled fluid pump 48 and the subcooling pump 100 may both be running.Additionally, the first and fourth valves 38 and 44 are open, while thesecond and third valves 40 and 42 are closed. In such a configuration,the cooler 24 (e.g., cooling heat exchanger) and the chilled fluid pump48 are coupled to the load 14, while being isolated from the thermalstorage unit 36. Moreover, in such a configuration, the subcooling pump100 circulates cooling fluid 33 (e.g., water) from the bottom 49 of thethermal storage unit 36, through the subcooling heat exchanger 32, andback to the top 47 of the thermal storage unit 36, as indicated byarrows 102. In this manner, the cooling fluid 33 in the thermal storageunit 36 (e.g., stratified water tank) cools the refrigerant 25 of thecooling system 10 via the subcooling heat exchanger 32, therebyincreasing the cooling capacity of the cooling system 10. As will beappreciated, the cooling system 10 may be in the subcoolingconfiguration or subcooling mode (e.g., first and fourth valves 38, 44open, second and third valves 40, 42 closed) during times of peakelectrical prices and peak cooling load. For example, the illustratedembodiment may be in the subcooling configuration during the daytimeand/or during the evening in warm weather.

To enter the recharging mode from the subcooling mode, the chilled fluidpump 48 and the subcooling pump 100 may both be turned off.Additionally, the first and fourth valves 38 and 44 are closed. In thismanner, the cooler 24 (e.g., cooling heat exchanger) and the chilledfluid pump 48 may be isolated from the load 14. Once the first andfourth valves 38 and 44 are closed, the second and third valves 40 and42 are opened to connect the cooler 24 (e.g., cooling heat exchanger)and the chilled fluid pump 48 to the thermal storage unit 36. In someembodiments, the flow rate of the cooling fluid 33 may be increasedduring the recharge mode relative to the subcooling mode such that thechilled fluid 33 within the thermal storage unit 36 is mixed. With thesecond and third valves 40 and 42 opened, the chilled fluid pump 48 maybe turned on to pump cooling fluid 33 (e.g., water) through the cooler24 (e.g., cooling heat exchanger) as shown by arrows 54. As a result,the cooling fluid 33 (e.g., water) within the thermal storage unit 36may be cooled, thereby “recharging” the cooling capacity of the thermalstorage unit 36. As similarly discussed above, the cooling system 10 andsubcooling system 12 may be in the recharging mode when energy rates arelower (e.g., night time).

In order to revert back to the subcooling mode from the recharging mode,the chilled fluid pump 48 is once again turned off, the second and thirdvalves 40 and 42 are closed, and the first and fourth valves 38 and 44are opened. Thereafter, the chilled fluid pump 48 and the subcoolingpump 100 may both be turned on, and the cooling fluid 33 in the thermalstorage unit 36 may be circulated as shown by arrows 102 to cool therefrigerant 25 in the manner described above.

A feature of this embodiment of the cooling system 10 is that it allowsfor a pressure difference between portions of the cooling system 10,such as between the thermal storage unit 36 and the load circuit 23supplying the load 14, if valves 38, 40, 42, and 44 can provide positiveshut off. Examples of valves that can provide pressure isolation includebutterfly valves or ball valves. It may be desirable for the valves tobe motor-actuated to allow for automatic control of the system.Additionally, or in the alternative, manual valves may be utilized forpressure isolation. This pressure isolation feature may be particularlydesirable in multistory buildings wherein the thermal storage unit 36 islocated at ground level. In subcooling mode, valves 40 and 42 areclosed, which isolates the thermal storage unit 36 from the pressure ofthe load circuit 23 (e.g., building loop). The chilled fluid pump 48 maydirect the load fluid 22 through the cooler 24 at the pressure of theload circuit 23. In recharge mode, valves 38 and 44 are closed. Thechilled fluid pump 48 may direct the cooling fluid 33 through the cooler24 at a tank pressure (e.g., the pressure of the thermal storage unit36) different from the pressure of the load circuit 23. Interlocks(e.g., control logic of an automation controller) can be provided toensure that neither the second valve 40 nor the third 42 is openwhenever either the first valve 38 or the fourth valve 44 is open. Itmay also be desirable to include space in the thermal storage unit 36 tohandle the full system fluid volume (e.g., load fluid 22 and coolingfluid 33) without overflowing in case of a leaking valve (e.g., secondvalve 40, third valve 42). The pressure-isolation characteristics ofpresent embodiments may eliminate or limit the cost and performancepenalties that typically accompany other options (e.g., a water-to-waterheat exchanger, a high-pressure water storage tank, or a supportstructure required to locate the tank physically higher). Presentembodiments facilitate packaging of components to simplify installationin the field. For example all the pumps and valves can be packaged withthe subcooling system 12 in a single unit, which eliminates field pipingand wiring and allows the controls of the pumps and valves to beintegrated into a chiller control (e.g., automation controller). Inaddition, the subcooling circuit 34 and a recharge conduit 35 mayconnect through a tee 104 to a single pipe 106 to the top 47 of thethermal storage unit 36. Similarly, a single pipe 108 communicativelycoupled to the bottom 49 of the thermal storage unit 36 can be provided.This setup means that only four fluid (e.g., water) connections areperformed at installation. These could be load connections 110 forsupply and return of the load fluid 22 with the load 14 and tankconnections 112 to the top 47 and the bottom 49 of the thermal storageunit 36. The piping for the thermal storage unit 36 may be inexpensive(e.g., plastic) pipe in embodiments with only a low fluid pressure.

FIG. 4 is an embodiment of the cooling system 10 having the refrigerantcircuit 20 and the subcooling system 12, where the subcooling system 12has multiple thermal storage units 36. More specifically, theillustrated embodiment includes two thermal storage units 36 (e.g.,stratified water tanks) and associated valves 120 so that one thermalstorage unit 36 can recharge while the other thermal storage unit 36 issupplying the cooling fluid 33 to the one or more subcooling heatexchangers 32. In this manner, the thermal storage units 36 can becontinually recharged throughout the day. Furthermore, the illustratedembodiment reduces the size of each thermal storage unit 36, and mayincrease efficiency of the subcooling system 12. For example, the valves120 may be controlled so that the cooling fluid 33 is drawn from a firstthermal storage unit 122 until the average temperature of the coolingfluid 33 of the first thermal storage unit 122 reaches a subcoolerthreshold temperature (e.g., temperature of the load fluid 22). Then,the cooling fluid 33 may be drawn from a second thermal storage unit 124while the cooling fluid 33 of the first thermal storage unit 122recharges (e.g., cools) via the cooler 24. The valves 120 illustrated inFIG. 4 may include the first, second, third, and fourth valves 38, 40,42, and 44 described above. The first valve 38 is between the cooler 24and the load 14, each second valve 40 is between the cooler 24 and arespective thermal storage unit 36, each third valve 42 is between arespective thermal storage unit 36 and the chilled fluid pump 48, andthe fourth valve is between the load 14 and the chilled fluid pump 48.

FIG. 5 is a schematic of an embodiment of the cooling system 10 havingat least one refrigerant circuit 20 and the subcooling system 12,wherein the subcooling system 12 includes a stratified fluid tank 138 asthe thermal storage unit 36. Specifically, the illustrated embodimentincludes two subcooling loops 140 that share the common stratified fluidtank 138. Additionally, the stratified fluid tank 138 includes amoveable partition 142 to separate cold cooling fluid 144 (e.g., coldwater) from warm cooling fluid 146 (e.g., warm water) within the thermalstorage unit 36. When the subcooling system 12 is configured in thesubcooling mode, both subcooling pumps 100 (e.g., a first pump 148 and asecond pump 150) may operate to move the cold cooling fluid 144 from thebottom 49 of the stratified fluid tank 138 through each of thesubcooling heat exchangers 32 (e.g., a first subcooling heat exchanger152 and a second subcooling heat exchanger 154). In some embodiments,each subcooling heat exchanger 32 may be fluidly coupled to a separaterefrigerant circuit 20 (e.g., first refrigerant circuit, secondrefrigerant circuit). Alternatively, one or more of the subcooling heatexchangers may be fluidly coupled to a common refrigerant circuit 20, asillustrated in FIG. 4. The subcooling heat exchangers 32 may be coupledto the same or a different refrigerant circuit 20 relative to therefrigerant circuit 20 with the cooler 24 that recharges (e.g., cool)the cooling fluid 33.

When the subcooling system 12 is configured in the recharge mode, achilled fluid pump 156 may circulate the warm cooling fluid 146 from thetop 47 of the stratified fluid tank 138 through the cooler 24, which ispart of a refrigerant circuit 20 (e.g., first refrigerant circuit) ofthe cooling system 10, as described above. The cooling fluid 33 (e.g.,water) exiting the cooler 24 is directed to two valves (e.g., a secondvalve 40A and a second valve 40B). As shown, the second valve 40Adirects the cooling fluid 33 to the top 47 of the stratified fluid tank138 from the cooler 24, and the second valve 40B directs the coolingfluid 33 to the bottom 49 of the stratified fluid tank 138 from thecooler 24. At the beginning of the recharge mode, the second valve 40Ais opened and the second valve 40B is closed so that the warm coolingfluid 146 (e.g., warm water) above the partition 142 is cooled first.Once the stratified fluid tank 138 is cooled to the point where thetemperature of the cooling fluid 33 (e.g., warm cooling fluid 146)leaving the stratified fluid tank 138 (e.g., out of the top 47 of thestratified fluid tank 138) is near a predetermined value, the secondvalve 40B is opened to allow cooling fluid 33 (e.g., cold cooling fluid144) into the bottom 49 of the stratified fluid tank 138 below thepartition 142. The second valve 40A and the second valve 40B may becontrolled by a programmed automation controller 52, as is the case forother control schemes and processes described herein. Moreover, asdescribed above with FIG. 2, one or more sensors 50 configured tomeasure operating parameters of the cooling fluid 33 may providefeedback to the controller 52. The controller 52 may utilize thefeedback to control the first and second valves 160. When the secondvalve 40B is opened, the second valve 40A may be closed, which causesthe cooling fluid 33 (e.g., warm cooling fluid 146) at the top 47 of thestratified fluid tank 138 to be drained, and the stratified fluid tank138 to fill with cold cooling fluid 144 at the bottom 49 of thestratified fluid tank 138. Once the stratified fluid tank 138 is filledwith cold cooling fluid 144 below the partition 142, the cooler 24 maybe shut down as the stratified fluid tank 138 is recharged. The cooler24 may not be shut down if the cooler 24 is otherwise coupled to arefrigerant circuit 20 configured to cool a load 14.

In certain embodiments, the subcooling system 12 may include afree-cooling heat exchanger. As will be appreciated, in certainenvironments, such as deserts, ambient air temperatures may besufficiently low to enable air cooling of the cooling fluid 33 withinthe thermal storage unit 36 via a free-cooling heat exchanger 162. Thefree-cooling heat exchanger 162 may be located in addition to or inplace of the cooler 24 between the chilled fluid pump 156 and the firstand second valves 158, 160. As such, the cooling fluid 33 may be furthercooled by ambient air before it enters the cooler 24. Additionally or inthe alternative, the same or a different free-cooling heat exchanger 162may be located in the one or more subcooling loops 140 with thesubcooling heat exchangers 152 and 154. In such a configuration, one ormore valves 164 may enable pumps 148 and 150 to draw cooling fluid 33(e.g., warm cooling fluid 146) from the top 47 of the thermal storageunit 36 through the free-cooling heat exchanger 162. Furthermore, afree-cooling heat exchanger 162 may be located in a separate loop withits own pump 166. In such an embodiment, the connections of the separateloop may be positioned near the top 47 of the thermal storage unit 36 sothat the separate free-cooling loop cools the warmest fluid (e.g., warmcooling fluid 146) from the thermal storage unit 36.

FIGS. 6-8 are schematic representations of the thermal storage unit 36(e.g., stratified fluid tank 138) shown in FIG. 5. For example, FIG. 6is a side cross-sectional view of the stratified fluid tank 138.Specifically, the illustrated stratified fluid tank 138 is a cylindricaltank having the moveable partition 142 that separates cold cooling fluid144 and warm cooling fluid 146. The moveable partition 142 may include athermal insulation layer 180 with a weight 182. As will be appreciated,the weight 182 may give the thermal insulation layer 180 a slightlynegative buoyancy relative to the cooling fluid 33. As discussed herein,portions of the cooling fluid 33 may be identified by relativetemperature, where a cold cooling fluid 144 has a lower temperature thana warm cooling fluid 146. As may be appreciated, the stratified fluidtank 138 separates the cold cooling fluid 144 from the warm coolingfluid 146. The cold cooling fluid 144 may be utilized with one or moresubcooling heat exchangers 32 to subcool a refrigerant 25, where thecooling fluid 33 enters the subcooling heat exchanger 32 as the coldcooling fluid 144 and exits the subcooling heat exchanger 32 as the warmcooling fluid 146. The warm cooling fluid 146 may be cooled during therecharge mode by circulation through the cooler 24 or free-cooling heatexchanger 162, thereby returning the cooling fluid 33 to the thermalstorage unit 36 (e.g., stratified fluid tank 138) as cold cooling fluid144.

The stratified fluid tank 138 further includes a liner 184. Morespecifically, the liner 184 is an elastic, flexible, and watertightliner 184 that is coupled to the moveable partition 142 and extendsupward to the top 47 of the stratified fluid tank 138. The liner 184 isattached to the top 47, to a wall 185 of the stratified fluid tank 138,or to a float. Additionally, the liner 184 has two layers 186 that arerolled up and coupled to one another (e.g., in a toroidal roll 188). Forexample, one layer 186 may form a flexible tube that is attached to theinside of the stratified fluid tank 138 near the top 47 of thestratified fluid tank 138. The other layer 186 forms another flexibletube that is attached to the circumference of the moveable partition 142(e.g., thermal insulation layer 180).

FIG. 7 is a top view of the stratified fluid tank 138 of FIG. 5. Asshown, the thermal insulation layer 180, the liner 184, and an outerwall 200 of the stratified fluid tank 138 may be generally concentric.Furthermore, FIG. 8 illustrates a cross-sectional view of the toroidalroll 188 formed by the two layers 186 of the liner 184, taken along line8-8 of FIG. 6. As indicated by arrow 210, each layer 186 of the liner184 may be in tension. That is, the thermal insulation layer 180 and theweight 182 may apply a tension force on the liner 184. In certainembodiments, the thickness of the liner 184, the diameter of thetoroidal roll 188, the diameter of the thermal storage unit 36, and/orthe size of the weight 182 may be selected to achieve a desired tensionin the liner 184. As may be appreciated, the stratified fluid tank 138is not limited to a cylindrical tank. In some embodiments, thestratified fluid tank 138 may have other cross-sectional shapes, such asan ellipse, rectangle, pentagon, hexagon, or another shape.

As mentioned above, the illustrated moveable partition 142 creates afluid-sealed boundary between the cold cooling fluid 144 and the warmcooling fluid 146 within the stratified fluid tank 138. As will beappreciated, such a design may improve control of the partition 142position. For example, while the weight 182 provides a slightly negativebuoyancy on the moveable partition 142, the curl (e.g., the spring forcethat acts to roll up the toroidal roll 188) of the liner 184 may balancethe negative buoyancy caused by the weight 182 when the levels of coldcooling fluid 144 and the warm cooling fluid 146 are approximately equalwithin the stratified fluid tank 138. Furthermore, in suchcircumstances, the tension on both sides of the liner 184 may be atequilibrium, such that the moveable partition 142 is relativelystationary. As cooling fluid 33 (e.g., water) is pumped into one side ofthe thermal storage unit 36 (e.g., the cold cooling fluid 144 side orthe warm cooling fluid 146 side), the moveable partition 142 may move inresponse until approximately equal tension is re-established. The resultis that the moveable partition 142 naturally seeks an equilibriumposition without any special controls.

In certain embodiments, the illustrated configuration may be applicableto the storage of other liquids, such as gasses, slurries, and otherfluid materials in one or more thermal storage units 36. Furthermore,while the embodiment illustrated in FIGS. 6-8 shows one moveablepartition 142, other embodiments of the thermal storage unit 36 may haveother numbers of moveable partitions 142 within a single tank. Forexample, the thermal storage unit 36 may include an upper partition anda lower partition. In such an embodiment, the upper partition may have asmaller diameter than the lower partition, and an upper liner for theupper partition may be positioned inside of a lower liner for the lowerpartition. As a result, the thermal storage unit 36 may have threeseparate layers or reservoirs of cooling fluid 33. That is, a firstreservoir of cooling fluid 33 (e.g., warm water exiting the subcoolingheat exchanger 32 at a temperature greater than approximately 60° F.)may be above the upper partition, a second reservoir of cooling fluid 33(e.g., water at an intermediate temperature between approximately thetemperature of the warm water in the first reservoir and the temperatureof the cold water in the third reservoir) may be between the upper andlower partitions, and a third reservoir of cooling fluid 33 (e.g., coldwater at a temperature between approximately 32 to 50° F.) may be belowthe lower partition. The temperature of the warm water exiting thesubcooling heat exchanger 32 may be approximately the temperature of therefrigerant 25 exiting the condenser 28 or a maximum design temperatureof the conduit carrying the warm water, whichever is lower. Furthermore,other embodiments of the thermal storage unit 36 may have more than twopartitions.

FIG. 9 is a schematic of an embodiment of the cooling system 10 havingat least one refrigerant circuit 20 and the subcooling system 12, wherethe thermal storage unit 36 includes multiple fluid connections 220arranged vertically across the thermal storage unit 36 (e.g., stratifiedfluid tank 138). The vertically arranged fluid connections 220 enableonly the cooling fluid 33 (e.g., warm water) near the top 47 of thethermal storage unit 36 to be cooled by the cooling fluid 33 that hasbeen recharged (e.g., cooled) by the cooler 24, leaving the coolingfluid 33 (e.g., cold water) at the bottom 49 of the thermal storage unit36 relatively undisturbed during a recharging mode. The controller 52may control (e.g., open, close) height valves 222 to inject coolingfluid 33 from the cooler 24 to one or more heights at a top portion 224where the warm cooling fluid 146 is approximately stratified in thethermal storage unit 36. Once the cooling fluid 33 at the top portion224 of the thermal storage unit 36 is cooled down to a thresholdtemperature, cooling fluid 33 (e.g., cold water) from the cooler 24 maybe directed to the bottom 49 of the thermal storage unit 36 through abottom valve 226. As may be appreciated, the cooling system 10 of FIG. 9may have a similar arrangement of the first, second, third, and fourthvalves 38, 40, 42, and 44 as described above with FIG. 3. The firstvalve 38 is between the cooler 24 and the load 14, the second valve 40is between the cooler 24 and the thermal storage unit 36, the thirdvalve 42 is between the thermal storage unit 36 and the chilled fluidpump 48, and the fourth valve is between the load 14 and the chilledfluid pump 48.

FIG. 10 is a schematic of the cooling system 10 having the refrigerantcircuit 20 and the subcooling system 12, where the subcooling system 12includes multiple thermal storage units 36 coupled in series. During asubcooling (e.g., discharge) mode, subcooling pumps 100 circulatecooling fluid 33 from one or more thermal storage units 36 through oneor more subcooling heat exchangers 32 of one or more refrigerantcircuits 20 to the top 47 of a first thermal storage unit 240 (e.g., afirst tank). The cooling fluid 33 may be cold cooling fluid 144 uponentering the subcooling heat exchangers 32, and may exit as warm coolingfluid 146 upon absorbing heat from the refrigerant 25 of the one or morerefrigerant circuits 20. In some embodiments, the first, second, andthird thermal storage units 240, 242, and 244 may begin operation eachsubstantially filled with cold cooling fluid 144. During the subcoolingmode, cold cooling fluid 144 flows from the third thermal storage unit244 to the one or more subcooling heat exchangers 32, and returns to thefirst thermal storage unit 240 as warm cooling fluid 146. As may beappreciated, cooling fluid 33 (e.g., cold cooling fluid 144) flows fromthe second thermal storage unit 242 to the third thermal storage unit244 to maintain a desired level of cooling fluid 33 (e.g., cold coolingfluid 144) in the third thermal storage unit 244. Likewise, coolingfluid 33 (e.g., cold cooling fluid) flows from the first thermal storageunit 240 to the second thermal storage unit 242 to maintain a desiredlevel of cooling fluid 33 (e.g., cold cooling fluid 144) in the secondthermal storage unit 242. The flow rate of cooling fluid between thefirst, second, and third thermal storage units 240, 242, and 244 may beapproximately the same, thereby maintaining the initial volume ofcooling fluid 33 within each thermal storage unit. As may beappreciated, the each thermal storage unit may stratify the coolingfluid 33 such that the cold cooling fluid 144 is near the bottom 49 todrain into the next thermal storage unit, and the warm cooling fluid 146is near the top 47.

The first thermal storage unit 240 fills with warm cooling fluid 146(e.g., warm water) from the one or more subcooling heat exchangers 32 asthe cold cooling fluid 144 (e.g., cold water) drains to the top 47 ofthe second thermal storage unit 242 from the bottom 49 of the firstthermal storage unit 240. When the first thermal storage unit 240 isfull of warm cooling fluid 146, additional warm cooling fluid 146 fromthe one or more subcooling heat exchangers 32 leads warm cooling fluid146 to flow from the bottom 49 of the first thermal storage unit 240 tothe top 47 of the second thermal storage unit 242. Once the secondthermal storage unit 242 is full of the warm cooling fluid 146 (e.g.,warm water) and substantially empty of the cold cooling fluid 144,additional warm cooling fluid 146 added to the second thermal storageunit 242 leads warm cooling fluid 146 to flow from the bottom 49 of thesecond thermal storage unit 242 to the top 47 of the third thermalstorage unit 244. Therefore, as the cold cooling fluid 144 issequentially drained from the first, second, and third thermal storageunits 240, 242, and 244 to flow through the one or more subcooling heatexchangers 32, warm cooling fluid 146 from the one or more heatexchangers 32 sequentially fills the first, second, and third thermalstorage units 240, 242, and 244 during the subcooling mode. Eventually,warm cooling fluid 146 may fill at least a portion of the third thermalstorage unit 244 until a recharge mode begins to cool at least a portionof the cooling fluid 33.

As may be appreciated, the cooling system 10 of FIG. 10 may have asimilar arrangement of the first, second, third, and fourth valves 38,40, 42, and 44 as described above with FIG. 3. The first valve 38 isbetween the cooler 24 and the load 14, the second valve 40 is betweenthe cooler 24 and the thermal storage units 36, the third valve 42 isbetween the thermal storage units 36 and the chilled fluid pump 48, andthe fourth valve is between the load 14 and the chilled fluid pump 48.Valves 246 allow for cooling fluid 33 to bypass one or more of thethermal storage units 240, 242, and 244 during a recharging mode. Thatis, the cooling fluid 33 of each thermal storage unit 240, 242, and 244may be recharged separately. For example, if only the first thermalstorage unit 240 contains warm cooling fluid, then a fifth valve 248between the second valve 40 and the first thermal storage unit 240 mayopen, and sixth and seventh valves 250 and 252 may remain closed so asto allow for cooling/recharging of only the cooling fluid 33 of thefirst thermal storage unit 240. If the first thermal storage unit 240 isfull of warm cooling fluid 146, and the second thermal storage unit 242is partially full of warm cooling fluid 146, then the fifth valve 248may be opened first to allow the cooling fluid 33 in the first thermalstorage unit 240 to cool down to a temperature near the averagetemperature of the cooling fluid 33 in the second thermal storage unit242. Then, the sixth valve 250 between the second valve 40 and thesecond thermal storage unit 242 may be opened, and the fifth valve 248may be closed to allow the first thermal storage unit 240 and/or thesecond thermal storage unit 242 to be cooled or recharged. Similarly,once the first and second thermal storage units 240 and 242 are cooledto a temperature near the average temperature of the cooling fluid inthe third thermal storage unit 244, the fifth and sixth valves 248 and250 may be closed while the seventh valve 252 between the second valve40 and the third thermal storage unit 244 is opened to allow for coolingor recharging of the third thermal storage unit 244, or each of thefirst, second, and third thermal storage units 240, 242, and 244.Operation of the valves 246, as discussed above, may be controlled by anautomation controller 52 based on measurements from sensors (e.g.,temperature sensors and level sensors) positioned in the thermal storageunits 240, 242, and 244. In some embodiments, thermal storage units 36in series may be utilized in a similar manner to a stratified storagetank 138, as described in FIG. 5. That is, separate thermal storageunits 36 may be utilized rather than the movable partition 142, wherethe separate thermal storage units 36 may be used to at least partiallyseparate the warm cooling fluid 146 from the cold cooling fluid 144.

FIG. 11 is a schematic of an embodiment of the cooling system 10 havingthe refrigerant circuit 20 and the subcooling system 12, where thethermal storage unit 36 of the subcooling system 12 includes multipletanks to thermally isolate cold cooling fluid 144 from warm coolingfluid 146. The thermal storage unit 36 may include a first tank 253, asecond tank 254, and a third tank 255, as well as flow control valves256 that may be controlled to isolate the cooling fluid 33 flow for eachtank. The first, second, and third tanks 253, 254, and 255 may behorizontally arranged, as shown in FIG. 11, or vertically arranged withthe third tank 255 above the second tank 254, and the second tank 254above the first tank 253. In some embodiments, each tank of the first,second, and third tanks 253, 254, and 255 may have a vent to the ambientenvironment, thereby enabling the cooling fluid 33 within each tank tobe at approximately atmospheric pressure. In some embodiments, each tankof the first, second, and third tanks 253, 254, and 255 may bepressurized above atmospheric pressure.

In some embodiments, the flow control valves 256 may be controlled toenable the cooling fluid 33 in the second tank 254 and/or the third tank255 to be recharged (e.g., cooled) while the first tank 253 suppliescold cooling fluid 144 to the subcooling heat exchanger 32 as shown byarrows 102. The first tank 253 supplies cold cooling fluid 144 to thesubcooling pump 100 during operation in a subcooling mode. The coldcooling fluid 144 absorbs heat from the refrigerant 25 in the subcoolingheat exchanger 32, thereby exiting the subcooling heat exchanger 32 aswarm cooling fluid 146. The warm cooling fluid 146 from the subcoolingheat exchanger 32 flows to the third tank 255. Accordingly, duringsubcooling mode, the first tank 253 has primarily cold cooling fluid144, and warm cooling fluid 146 is added to the third tank 355. As thecold cooling fluid 144 empties from the first tank 253 via thesubcooling pump 100 through the subcooling heat exchanger 32, the firstand second control valves 257, 258 may open to fill the first tank 253with any cold cooling fluid 144 from the second tank 254. The firstcontrol valve 257 is between the second valve 40 and the first tank 253,and the second control valve 258 is between the second valve 40 and thesecond tank 254. The third tank 255 may be approximately 30 to 50percent larger than either the first tank 253 or the second tank 254. Insome embodiments, the volume of cooling fluid in the first, second, andthird tanks 253, 254, and 255 may be controlled to enable the totalcooling fluid volume may be held within the third tank 255, thesubcooling circuit 34, and one of first tank 253 or the second tank 255.

Warm cooling fluid 146 from the third tank 255 may be directed to thesecond tank 254 as the third tank 255 fills with warm cooling fluid 146from the subcooling heat exchanger 32. For example, a second controlvalve 258 and a third control valve 265 may open, the second valve 40and a fifth control valve 267 may be closed, and a transfer pump 259 maypump at least a portion of the warm cooling fluid 146 from the thirdtank to the second tank 254, as shown by arrow 103. The third controlvalve 265 along arrows 103, 105, and 109 between the third tank 255 andthe transfer pump 259 or the third valve 42. Additionally, or in thealternative, the third control valve 265 and a fourth control valve 266may be opened while the third valve 42 is closed to enable at least aportion of the warm cooling fluid 146 from the third tank 255 to thesecond tank 254, as shown by arrow 105. The fourth control valve 266 isalong arrows 103 and 105 between the second tank 254 and the transferpump 259 or the third valve 42. Accordingly, continued operation in thesubcooling mode without recharge may substantially fill the second andthird tanks 254, 255 with warm cooling fluid 146, while the first tank253 is substantially emptied of the cold cooling fluid 144.

As may be appreciated, the cooling system 10 of FIG. 11 may have asimilar arrangement of the first, second, third, and fourth valves 38,40, 42, and 44 as described above with FIG. 3. The first valve 38 isbetween the cooler 24 and the load 14, the second valve 40 is betweenthe cooler 24 and the thermal storage units 36, the third valve 42 isbetween the thermal storage units 36 and the chilled fluid pump 48, andthe fourth valve is between the load 14 and the chilled fluid pump 48.During a recharge mode, the control valves 256 and the first, second,third, and fourth valves 38, 40, 42, and 44 may be controlled to coolthe cooling fluid 33 (e.g., warm cooling fluid 146) in the second tank254 and the third tank 255 separately. For example, the first and fourthvalves 38, 44 may close and the second and third valves 40, 42 may opento fluidly couple the subcooling circuit 34 with the cooler 24. Torecharge the cooling fluid of the second tank 254 upon coupling thesubcooling circuit 34 with the cooler 24, the second control valve 258and fourth control valve 266 are opened, and the first, third, and afifth control valve 257, 265, and 267 are closed to enable the flowshown by arrow 107. The fifth control valve 267 is between the secondvalve 40 and the third tank 255. Therefore, the cooling fluid 33 of thesecond tank 254 may be drawn toward the chilled fluid pump 48, as shownby arrow 54, and pumped through the chiller 24 and back to the secondtank 254, as shown by arrow 111, to decrease the temperature of thecooling fluid within the second tank 254. During the recharge of thecooling fluid 33 in the second tank 254, the first tank 253 maysimultaneously supply cold cooling fluid 144 to the subcooling heatexchanger 32, thereby subcooling the refrigerant 25 and increasing thewarm cooling fluid 146 in the third tank 255. When the cooling fluid 33in the second tank 254 reaches a desired temperature (e.g., temperatureof the cold cooling fluid 144), the fourth control valve 266 may beclosed, and the first and second control valves 257, 258 are controlledto fill the first tank 253 with the cooling fluid 33 from the secondtank 254.

The warm cooling fluid 146 of third tank 255 may be recharged viamultiple valve configurations. In some embodiments, at least a portionof the warm cooling fluid 146 of the third tank 255 may be transferreddirectly to the second tank 254, as discussed above and shown by arrows103 or 105. The warm cooling fluid 146 received by the second tank 254may then be recharged as shown by arrows 107, 54, and 111. In someembodiments, the second and third control valves 258, 265 may be openedwhile the first, fourth, and a fifth control valve 257, 266, 267 areclosed, thereby enabling the flow shown by arrow 109. The chilled fluidpump 48 directs the warm cooling fluid 146 from the third tank 255, asshown by arrows 109 and 54, through the cooler 24 and into the secondtank 254 as cold cooling fluid 144, as shown by arrow 111. Moreover, insome embodiments, the third control valve 265 and the fifth controlvalve 267 are opened while the first, second, and fourth control valves257, 258, and 266 are closed, thereby enabling the flow shown by arrow109. The chilled fluid pump 48 directs the warm cooling fluid 146 fromthe third tank, as shown by arrows 109 and 54, through the cooler 24 andinto the third tank 255 as cold cooling fluid 144, as shown by arrow113. Any of the above valve configurations may be utilized to cool thewarm cooling fluid 146 of the third tank 255. In some embodiments, coldcooling fluid 144 from the first tank 253 may not flow through thesubcooling heat exchanger 32, such as by closing a sixth control valve268 between the first tank 253 and the subcooling pump 100, therebyreducing the warm cooling fluid 146 added to the third tank 255 whilethe third tank 255 is recharged. Additionally, or in the alternative, aseventh control valve 269, located between the sixth control valve 268and the third valve 42, may be opened to enable cold cooling fluid 144from the first tank 253 to be directed through the cooler 24 with thewarm cooling fluid 146. Accordingly, the temperature of the coolingfluid 33 in the third tank 255 may be decreased to a desired temperature(e.g., temperature of the cold cooling fluid 144).

In some embodiments, the cooling fluid 33 of the third tank 255 may becooled while subcooling the refrigerant 25 without adding warm coolingfluid 146 to the cooling fluid 33 that is being cooled in the third tank255. For example, a fourth tank 270 may receive the warm cooling fluid146 from the subcooling heat exchanger 32 while the third tank 255 isrecharged. In another embodiment, the third tank 255 may be a stratifiedfluid tank with a partition as described above, thereby enabling thewarm cooling fluid 146 entering the third tank 255 to be separated fromthe cooling fluid 33 being recharged. In another embodiment, thesubcooling heat exchanger 32 may not receive cold cooling fluid 144 fromthe first tank 253 while recharging the third tank 255. Accordingly, thefirst, second, and third tanks 253, 254, and 255 may be utilized toreduce or eliminate mixing of cold cooling fluid 144 with warm coolingfluid 146 within any particular tank.

FIG. 12 is a schematic of an embodiment of the cooling system 10 havingthe refrigerant circuit 20 and the subcooling system 12, where thethermal storage unit 36 does not include a tank. More specifically, thethermal storage unit 36 in the illustrated embodiment includes a groundloop 260 (e.g., a subterranean conduit or conduit below a surface 264 ofthe earth which carries the cooling fluid 33). In certain embodiments,the ground loop 260 may thermally isolate warm cooling fluid 146 andcold cooling fluid 144 to improve thermal storage capability. Forexample, the ground loop 260 may include a horizontal loop or multiplevertical loops 262 in series to help thermally isolate warm coolingfluid 146 and cold cooling fluid 144. As may be appreciated, the coolingsystem 10 of FIG. 12 may have a similar arrangement of the first,second, third, and fourth valves 38, 40, 42, and 44 as described abovewith FIG. 3. The first valve 38 is between the cooler 24 and the load14, the second valve 40 is between the cooler 24 and the ground loop260, the third valve 42 is between the ground loop 260 and the chilledfluid pump 48, and the fourth valve is between the load 14 and thechilled fluid pump 48.

FIG. 13 is a schematic of an embodiment of the cooling system 10 havingthe refrigerant circuit 20 and the subcooling system 12, where thesubcooling system 12 is a “once-through” system. In other words, theillustrated embodiment of the subcooling system 12 directs a coolingfluid 33 (e.g., water) through the subcooling system 12 once, and thecooling fluid 33 is not necessarily re-circulated. For example, thecooling fluid 33 (e.g., water) may be supplied by a fluid source 280,such as ground water or municipal water. The cooling fluid 33 exitingthe subcooling heat exchanger 32 as warm cooling fluid 146 may be usedfor other applications. For example, the warm cooling fluid 146 may flowto a water heater 282 to heat further or to preheat water, to areservoir 284 for present or future use with an irrigation system 286,or other uses. As will be appreciated, the illustrated embodiment may beparticularly applicable in environments or locations where a fluidsource of cold cooling fluid 144, such as cool ground water, isavailable and/or abundant.

FIG. 14 is a schematic of an embodiment of the cooling system 10 havingthe multiple refrigerant circuits 20 and the subcooling system 12. Themultiple refrigerant circuits 20 has multiple coolers 24, and thesubcooling system 12 has multiple subcooling heat exchangers 32. In someembodiments, the coolers 24 may be fluidly coupled in the respective oneor more refrigerant circuits 20 in a parallel configuration, as shown bycoolers 312 and 314. Additionally, or in the alternative, the subcoolingheat exchangers 32 may be coupled in the respective one or morerefrigerant circuits 20 in a parallel configuration, as shown bysubcooling heat exchangers 340 and 342. As may be appreciated, thecoolers 24 and subcooling heat exchangers 32 may be fluidly coupled tothe one or more refrigerant circuits 20 and/or to the subcooling system10 in various configurations. Accordingly, the cooling system 10 mayhave additional flexibility in connecting different subcooling heatexchangers 32 to the thermal storage unit 36 for subcooling therefrigerant 25, additional flexibility in connecting different coolers24 to the load 14 for cooling the load 14, and/or additional flexibilityin connecting different coolers 24 to the thermal storage unit 36 forrecharging the cooling fluid 33.

For example, if valves 300 and 302 are closed and valves 304, 306, 308,and 310 are opened, then each of the coolers 312, 314, and 316 iscoupled to the load 14 to cool the load fluid 22, and each of thecoolers 312, 314, and 316 is isolated from the thermal storage unit 36.As shown, each of the coolers 312, 314, and 316 has a corresponding loadpump 318, 320, and 322, respectively, and a corresponding check valve324, 326, and 328, respectively, to provide a fluid (e.g., load fluid22, cooling fluid 33) flow through each cooler 312, 314, and 316.Additionally, a supply pump 330 may move load fluid 22 to the load 14.Subcooling pumps 332, 334, and 336 pump cooling fluid 33 (e.g., water)from the thermal storage unit 36 to the subcooling heat exchangers 32,which are in refrigerant circuits 20 with the coolers 312, 314, and 316as discussed above. For example, the subcooling pump 332 may supplycooling fluid 33 to a subcooling heat exchanger 32 that is fluidlycoupled to the cooler 316, the subcooling pump 334 may supply coolingfluid 33 to a subcooling heat exchanger 32 that is fluidly coupled tothe coolers 314 and 312, and the subcooling pump 336 may supply coolingfluid 33 to a subcooling heat exchanger 32 that is fluidly coupled tothe coolers 314 and 316. In certain embodiments, check valves 338, 340,and 342 may also be included with the subcooling loops.

The cooling system 10 illustrated in FIG. 14 may enable the coolingfluid 33 of the thermal storage unit 36 to be simultaneously rechargedvia one or more coolers 312, 314, and 316 while subcooling therefrigerant 25 of one or more refrigerant circuits 20 via one or moresubcooling heat exchangers 32. In other words, the cooling system 10 mayoperate in the recharge mode and subcooling mode at the same time. Inthe illustrated embodiment, the thermal storage unit 36 (e.g., watertank) may be recharged using cooler 316 by closing valves 308 and 310and opening valves 300 and 302, thereby isolating the thermal storageunit 36 from the coolers 312 and 314. As will be appreciated, to providepressure isolation, valves 308 and 310 should be closed before valves300 and 302 are opened. This configuration allows for cooler 316 to coolthe cooling fluid 33 (e.g., water) in the thermal storage unit 36 whilecoolers 312 and 314 supply load fluid 22 (e.g., chilled water) to theload 14. Similarly, valves 304 and 306 can be closed while valves 300,302, 308, and 310 are opened, thereby isolating the thermal storage unit36 from the cooler 312. In such a configuration, coolers 314 and 316 maycool the cooling fluid 33 in the thermal storage unit 36, while cooler312 supplies load fluid 22 (e.g., chilled water) to the load 14.

FIG. 15 is a schematic of an embodiment of the cooling system 10 havinga refrigerant loop 350 and the subcooling system 12, where thesubcooling system 12 may be suitable for trans-critical operation of therefrigerant 25 through the refrigerant loop 350. As may be appreciated,a trans-critical process may cool the refrigerant 25 to a subcooled(e.g., liquid) state, and may heat and/or pressurize the refrigerant 25to a supercritical state where liquid and gas phases of the refrigerant25 are indistinguishable. For example, in the illustrated embodiment,the cooling system 10 has a refrigerant loop 350, and the subcoolingsystem 12 has a first cooling fluid (e.g., water) loop 352 and a secondcooling fluid (e.g., water) loop 354. Similar to the refrigerant circuit20 described above, the refrigerant loop 350 circulates a refrigerant 25(e.g., carbon dioxide, R134a, R410A, R32, R1233ZD(E), R1233zd (E),R1234yf, R1234ze) and includes the cooler 24, the compressor 26, thesubcooling heat exchanger 32, and the expansion device 30. The cooler 24may be utilized to recharge the cooling fluid 33 (e.g., water) of thethermal storage unit 36. The illustrated refrigerant loop 350 includes acondenser coil 356 as the condenser 28, and a condenser fan 358 isconfigured to move air over the condenser coil 356, thereby cooling therefrigerant 25. The refrigerant loop 350 also includes an evaporatorcoil 360, in which the refrigerant 25 absorbs heat and at leastpartially evaporates. In some embodiments, the load fluid 22 (e.g.,return water 45) from the load 14 circulates through the evaporator 360to transfer heat to the refrigerant 25. An evaporator fan 362 may beconfigured to move air over the evaporator coil 360, thereby cooling theair and transferring heat to the refrigerant 25. In some embodiments,the air moving over the evaporator coil 360 is the load, such as in arefrigeration system.

A first cooling fluid loop 352 may subcool the refrigerant 25 of therefrigerant loop 350 via the subcooling heat exchanger 32. For example,the first cooling fluid loop 352 supplies the cooling fluid 33 (e.g.,cold water) from a lower tank 366 to the subcooling heat exchanger 32and to an upper tank 368 via a first pump 364. A second cooling fluidloop 354 may be cool (e.g., recharged) via circulation through thecooler 24. For example, the second cooling fluid loop 354 supplies thecooling fluid 33 (e.g., water) from the lower tank 366 to the cooler 24,and back to the lower tank 366. The thermal storage unit 36 may includethe lower tank 366 and the upper tank 368, where the upper tank 368 isarranged vertically above the lower tank 366. Specifically, the firstcooling fluid loop 352 includes a first pump 364 configured to pump thecooling fluid 33 through the first cooling fluid loop 352. That is, thefirst pump 364 draws the cooling fluid 33 from a bottom 365 of the lowertank 366 of the thermal storage unit 36, pumps the cooling fluid 33through the subcooling heat exchanger 32, and discharges the warmedcooling fluid 33 into the upper tank 368 of the thermal storage unit 36.A valve 370 is located between the lower tank 366 and the upper tank 368to complete the first cooling fluid loop 352. Similarly, the secondcooling fluid loop 354 includes a second pump 372 configured to pump thecooling fluid 33 through the second cooling fluid loop 354.Specifically, the second pump 372 draws cooling fluid 33 (e.g., water)from the bottom 365 of the lower tank 366, pumps the cooling fluid 33through the cooler 24, and discharges the cooling fluid 33 back into thelower tank 366.

During a discharge (e.g., cooling) mode of the illustrated embodiment,the refrigerant 25 in the evaporator 360 absorbs heat from the load 14.The compressor 26 increases the pressure of the refrigerant 25 anddirects the refrigerant 25 through the condenser 356 to reject heat tothe air drawn by the condenser fan 358. The first pump 364 moves coldcooling fluid 144 (e.g., cold water) from the bottom 365 of the lowertank 366, through the subcooling heat exchanger 32, and into the uppertank 368, thereby further cooling the refrigerant 25 before expansion bythe expansion device 30. An air vent 374 of the thermal storage unit 36enables air to move freely from a top 375 of the upper tank 368 to a 377top of the lower tank 366, such that the level of the cold cooling fluid144 in the lower tank 366 drops as the first pump 364 fills the uppertank 368 with warm cooling fluid 146 from the subcooling heat exchanger32.

At the beginning of the recharge mode of the illustrated embodiment, thevalve 370 may open between the upper tank 368 and the lower tank 366,thereby enabling warm cooling fluid 146 from the upper tank 368 to drainto the lower tank 366. During the recharge mode, the refrigerant 25through the refrigerant loop 350 may be utilized to primarily cool thecooling fluid 33 through the cooler 24 rather than to remove heat fromthe load 14. For example, as the warm cooling fluid 146 drains, theevaporator fan 362 may be turned off, and the second pump 372 may beturned on to move warm cooling fluid 146 from the lower tank 366,through the cooler 24, and back to the lower tank 366, thereby reducingthe temperature of the cooling fluid 33 within the lower tank 366. Insome embodiments, the first pump 364 may continue to direct coolingfluid 33 through the first cooling fluid loop 352 and the subcoolingheat exchanger 32 during the recharge mode, thereby sending warm coolingfluid 146 to the upper tank 368. Upon draining a desired amount (e.g.,25, 50, 75, 100 percent) of the warm cooling fluid 146 from the uppertank 368, the valve 370 may be closed, and the warm cooling fluid 146leaving the subcooling heat exchanger 32 may then accumulate in theupper tank 368 during the remainder of the recharge process. Once thelower tank 366 is cooled to a desired minimum temperature by circulatingthe cooling fluid through the second cooling fluid loop 354, therecharging process may be complete. Upon completion of the rechargingprocess, a majority of the cooling fluid 33 may be in the lower tank 366as cold cooling fluid 144, with the remainder of the cooling fluid 33being warm cooling fluid 146 in the upper tank 368.

As will be appreciated, the operation of the cooling system 10 and thesubcooling system 12 in discharge or recharge mode may depend on variousfactors. For example, for systems where thermal storage is lowerpriority, the sizes of the upper and lower tanks 368 and 366 may berelatively small, thereby enabling the cooling system 10 to operate inthe discharge mode for a brief time (e.g., approximately 1 hour orless). In such circumstances, it may be desirable to initiate a rechargemode when the cooling fluid level in the lower tank 366 reaches aminimum value. However, in embodiments where thermal storage is higherpriority, the upper and lower tanks 368 and 366 may be relatively largeand may be able to operate in a discharge mode for several hours withoutrecharging. In such circumstances, the recharge mode may be initiated atnight or other times when energy rates are reduced.

Furthermore, in certain embodiments, as discussed above, the thermalstorage unit 36 may include a single tank (e.g., stratified fluid tank138). As will be appreciated, such embodiments may utilize less spaceand may have lower initial equipment costs. In a single tank embodiment,the first cooling fluid loop 352 may discharge cooling fluid back to thetop of the lower tank 366, such as above a moveable partition.

FIG. 16 is a schematic pressure-enthalpy diagram for the refrigerant 25of the refrigerant loop 350 in the cooling system shown in FIG. 15.Specifically, loop 400 shows pressure and enthalpy of the refrigerant 25of the refrigerant loop 350 when the cooling system 10 is operating in adischarge mode, where the subcooling system 12 cools the refrigerant 25via the subcooling heat exchanger 32. Moreover, loop 402 illustrates thepressure and enthalpy of the refrigerant 25 of the refrigerant loop 350when the cooling system 10 is beginning to recharge the cooling fluid 33of the subcooling system 12. As shown by loop 402, the refrigerant 25may remain gaseous (e.g., outside the saturated vapor curve) throughoutthe loop 402. Loop 404 illustrates the pressure and enthalpy of therefrigerant 25 of the refrigerant loop 350 during a middle of therecharge of the cooling fluid 33 of the subcooling system 12, where therefrigerant 25 may change phases within the loop 404. Loop 406illustrates the pressure and enthalpy of the refrigerant 25 of therefrigerant loop 350 near an end of the recharge of the cooling fluid 33of the subcooling system 12. For comparison, loop 408 illustrates aconventional trans-critical vapor compression cycle without thesubcooling system 12.

As will be appreciated, the cooling system 10 with the refrigerant loop350 and the subcooling system 12 illustrated in FIG. 15 may reducelosses associated with the expansion process. More specifically, duringthe discharge mode the cooling fluid 33 of the subcooling system 12 maybe used to cool the trans-critical refrigerant fluid 25 of therefrigerant loop 350 via the subcooling heat exchanger 32 to atemperature that is near the evaporating temperature of thetrans-critical refrigerant 25. The energy in the cooling fluid 33 isthen rejected to the refrigerant 25 via the cooler 24 during therecharge mode, and the refrigerant 25 rejects the heat to the air viathe condenser 356. Furthermore, the upper and lower tank 368 and 366configuration of the embodiment shown in FIG. 15 may be incorporatedwith other embodiments described herein.

In the case of trans-critical operation there is no phase change (e.g.,gas to liquid) in the condenser 356, and the subcooler 32 cools atrans-critical refrigerant 25 instead of subcooling a condensed liquidrefrigerant. That is, the liquid cooling fluid may cool thetrans-critical refrigerant fluid 25 in the subcooler 32. In addition itis possible to operate the evaporator 360 and the expansion device 30when the temperature of the evaporator 360 exceeds the criticaltemperature of the refrigerant 25. Loop 402 in FIG. 16 is an example ofthis extreme operating condition where the refrigerant 25 does notcondense. Therefore the names of the components (e.g., evaporator 360,condenser 356) are intended to broadly include operation at conditionsthat exist at or above the refrigerant critical point.

FIG. 17 is a schematic of an embodiment of the cooling system 10 havingthe refrigerant circuit 20 and the subcooling system 12, where thesubcooling system 12 utilizes ice storage. In this embodiment, meltedwater from an ice storage tank 420 (e.g., thermal storage unit 36) isused for subcooling. Specifically, a subcooling pump 422 moves coldwater 423 from a bottom 425 of the ice storage tank 420, through thesubcooling heat exchanger 32, and back to a top 427 of the ice storagetank 420. In certain embodiments, the flow rate of the subcooling pump422 may be selected to create a stratified ice storage tank. That is,the flow rate may be slow so as to preserve the stratification of theice storage tank 420. Additionally, a glycol solution or otheranti-freeze liquid may be circulated through coils 424 in the icestorage tank 420 to produce ice. Specifically, valves 426 and 428 may beconfigured to regulate the glycol or other anti-freeze liquid flow.

During a recharge mode, valve 426 between the ice storage tank 427 and aglycol pump 423 closes glycol flow to the load 14 and directs it to abypass line 430 and to the glycol pump 432, as indicated by arrow 434.Additionally, in the recharge mode, valve 428 between the cooler 24 andthe ice storage tank 427 directs glycol through the coils 424 in the icestorage tank 420, as indicated by arrow 436. The recharge mode mayfreeze the cold water 423 to ice. In a discharge mode (e.g., coolingusing melted ice water 423), the valve 426 is open to the load 14 andclosed to the bypass line 430, as indicated by arrow 438. Additionally,valve 428 remains open to the coils 424 in the ice storage tank 420.Once the ice in the ice storage tank 420 has melted, valve 428 closesglycol flow to the coils 424 in the ice storage tank 420. At this point,the subcooling pump 422 can be operated to provide additional cooling(e.g., to the subcooling heat exchanger 32) using cold water (e.g.,melted ice water 423) from the bottom of the ice storage tank 420, inthe manner described above.

FIG. 18 is a schematic of an embodiment of the cooling system 10 havingthe refrigerant circuit 20 and the subcooling system 12, where thesubcooling system 12 has two thermal storage units 36 connected inparallel during recharge mode and connected in series in subcoolingmode. In the subcooling mode, warm cooling fluid 450 from the subcoolingheat exchanger 32 enters near the top 47 of a first thermal storage unit452 at a low flow rate to enable stratification of the cooling fluid 33into a warm layer 454 and a cool layer 456. Cold cooling fluid 33 exitsthe first thermal storage unit 452 near the bottom 49 of the firstthermal storage unit 452 through an inclined pipe 458 and enters thesecond thermal storage unit 460 near the top 47, as shown by the solidarrows 462. Cold cooling fluid 33 exits near the bottom 49 of the secondthermal energy storage unit 404 to the subcooling pump 100. The conduitscarrying the cooling fluid 33 during the subcooling mode are sized toenable the stratification of the first and the second thermal energystorage units 452, 460 via a relatively low flow rate. The arrangementof the inclined pipe 458 fluidly couples the first and second thermalstorage units 452, 460 in series during the subcooling mode withoututilizing valves to control the flow between the first and secondthermal storage units 452, 460.

In the recharge mode, cooling fluid 33 flows from the first and/or thesecond thermal storage units 452, 460 as shown by the dashed arrows 54.Chilled cooling fluid 33 from the cooler 24 enters through the inclinedpipe 458 and may split to flow to flow into the first and the secondthermal energy storage units 452 and 460. A first recharge valve 464coupled to the first thermal storage unit 452 may control the recharged(e.g., chilled) flow of cooling fluid 33 into the first thermal storageunit 452, and a second recharge valve 466 coupled to the second thermalstorage unit 460 may control the recharged (e.g., chilled) flow ofcooling fluid 33 into the second thermal storage unit 460. As may beappreciated, the chilled fluid pump 48 may direct the recharged chilledfluid 33 into the first and second thermal storage units 452, 460 at ahigher flow rate than the subcooling pump 100, thereby mixing thecooling fluid within the first and second thermal storage units 452, 460during the recharge mode. Cooling fluid 33 exits the first and secondthermal storage units 452, 460 through a conduit 468, and the chilledfluid pump 48 directs the combined cooling fluid flow through thechiller 24. A third recharge valve 470 coupled to the first thermalstorage unit 452 may control the flow of cooling fluid 33 from the firstthermal storage unit 452 to the chilled fluid pump 48, and a fourthrecharge valve 472 coupled to the second thermal storage unit 460 maycontrol the flow of cooling fluid 33 from the second thermal storageunit 460 to the chilled fluid pump 48. The first, second, third, andfourth recharge valves 464, 466, 470, and 472 may be selectively openedand closed to recharge the first thermal storage unit 452 and the secondthermal storage unit 460 at the same time. Additionally, or in thealternative, the first, second, third, and fourth recharge valves 464,466, 470, and 472 may be selectively opened and closed to recharge onlythe first thermal storage unit 452 or only the second thermal storageunit 460. While the first and second recharge valves 464, 466 are shownon the inclined pipe 458, it may be appreciated that other arrangementsof the first and second recharge valves 464, 466, such as within therespective first and second thermal storage units 452, 460, may enablethe recharge of one or both of the thermal storage units 452, 460.Likewise, while the third and fourth recharge valves 470, 472 are shownon the conduit 468, it may be appreciated that other arrangements of thethird and fourth recharge valves 464, 466, such as within the respectivefirst and second thermal storage units 452, 460, may enable the rechargeof one or both of the thermal storage units 452, 460. The first, second,third, and fourth recharge valves 464, 466, 470, and 472 may be include,but are not limited to butterfly valves. Similar configurations ofrecharge valves, inclined pipes, and conduits can be extended to morethan two thermal storage units.

In some embodiments, the conduit 468 may be coupled between the firstthermal storage unit 452 and the second thermal storage unit 460 in asimilar manner as the inclined pipe 458. That is, the conduit 468 mayform a substantially parallel pathway to the inclined pipe 458 in whicha first end of the conduit 468 is coupled near the bottom 49 of thefirst thermal storage unit 452 and an opposite second end of the conduit468 is coupled near the top 47 of the second thermal storage unit 460.This inclined configuration of the conduit 468 may enable the removal ofthe third and fourth recharge valves 470, 472. In the subcooling mode,the cooling fluid 33 from the bottom of the first thermal storage unit452 may flow through the conduit 468 and the inclined pipe 458 to alocation near the top 47 of the second thermal storage unit 460, asshown by the solid arrows 462. This inclined configuration of theconduit 468 enables warm cooling fluid 33 to fill the first thermalstorage unit 452 and cold cooling 33 to flow through the inclined pipe458 and the conduit 468 to the second thermal storage unit 460, suchthat the warm layer 454 substantially fills the first thermal storageunit 452. When the first thermal storage unit 452 is filled with warmcooling fluid, warm cooling fluid 33 may flow through the inclined pipe458 and the conduit 468 to form a stratified warm layer 454 and a coollayer 456 of cooling fluid 33 in the second thermal storage unit 460. Inthe recharge mode, the cooled cooling fluid 33 from the cooler 24 mayflow into the first and second thermal storage units 452, 460 throughthe inclined pipe 458, and the cooling fluid 33 may flow from the firstand second thermal storage units 452, 460 through the conduit 468 to berecharged (e.g., cooled) via the cooler 24. The inclined configurationof the conduit 468 may enable the removal of the third and fourthrecharge valves 470, 472 to control flow during subcooling and rechargemodes. As may be appreciated, some valves may be utilized to enableservicing or replacement of thermal storage units 36 and piping whileoperating with the remaining one or more thermal storage units 36.Additionally, or in the alternative, valves may be utilized forbalancing flow between the first and second thermal storage units 452,460 during recharge mode.

As will be appreciated, the systems and embodiments described above mayinclude variations in components, configurations, operating parameters,and so forth, which may depend on the particular application of thecooling system 10 with the refrigerant circuit 20 and the subcoolingsystem 12. For example, the compressors 26 described above may beconfigured for use with varying suction pressures. Such compressors 26may include variable-speed centrifugal compressors, variable-speedreciprocating compressors, variable-stroke linear compressors,compressors with magnetic bearings, and so forth. For reciprocating andlinear compressors, the discharge valve naturally compensates forchanges in pressure ratio. Additionally, at high suction pressure, itmay be desirable to reduce compressor capacity to prevent overload ofthe rest of the cooling system 10. Reduced compressor speed or reducedpiston stroke also prevents overloading the suction and discharge valvesfor the reciprocating and linear compressors.

Furthermore, in addition to including the subcooling heat exchanger 32in the refrigerant circuit (e.g., refrigerant circuit 20, refrigerantloop 350) of the cooling system 10, it may be desirable to make othermodifications to the cooling system 10. For example, a subcoolingsection from the condenser 28 may be removed, which may allow more spacefor condensation and/or a reduction in condenser 28 size and cost. Forair-cooled condensers, reducing the refrigerant charge in the condenser28 may have a similar effect. For other cooling systems 10, it may bedesirable to eliminate economizers to reduce costs, to reduce compressor26 load during peak conditions, and/or to increase the energy storagecapacity of the thermal storage unit 36 of the subcooling system 12.Likewise, it may be desirable to eliminate intercoolers found inmulti-stage centrifugal compressors or other multi-stage systems.

As described above, the cooling fluid flow rate of the subcooling system12 may be optimized to maximize efficiency of the subcooling system 12to cool the refrigerant 25 of the refrigerant circuit 20 of the coolingsystem 10. In certain embodiments, the cooling fluid flow rate throughthe subcooling heat exchanger 32 may be selected such that thetemperature change of the cooling fluid 33 across the subcooling heatexchanger 32 may be approximately equal to the temperature change of therefrigerant 25 across the subcooling heat exchanger 32. In someembodiments, the cooling fluid flow rate through the subcooling heatexchanger 32 may be selected such that the cooling fluid 33 exiting thesubcooling heat exchanger 32 is approximately the same temperature asthe refrigerant 25 entering the subcooling heat exchanger 32, and therefrigerant 25 exiting the subcooling heat exchanger 32 is approximatelythe same temperature as the cooling fluid 33 entering the subcoolingheat exchanger 32.

Additionally, as described with reference to FIG. 2 above, the systemmay include a variety of sensors 50 and a controller 52 (e.g., anautomation controller, programmable logic controller, distributedcontrol system, etc.) configured to operate various components (e.g.,valves) based on feedback measured by the sensors 50. It should beappreciated that the sensors 50 and controller 52, as well as othersensors and controllers, may be used with any of the embodimentsdescribed herein. For example, the sensors 50 may be configured tomeasure temperatures, pressures, flow rates, or other operatingparameters of the refrigerant circuit 20 and/or the subcooling system12. Additionally, the controller 52 may be configured to operate any ofthe components (e.g., valves, pumps) described herein or othercomponents based on measured feedback.

As discussed above, the refrigerant circuit 20 and the subcoolingsystems 12 described herein may improve efficiency of the cooling system10. Additionally, certain embodiments described above may have lowercosts (e.g., first costs and/or operating costs) than other systems. Forexample, equipment costs, energy costs, maintenance costs, and othercosts may be reduced. In some embodiments, thermal storage units 36 mayreduce the foot print at a worksite utilized for a given cooling load.For example, a cooling system with a 10,000 ton capacity utilizingradiators rather than thermal storage units may have a foot print ofapproximately 38,220 ft², whereas a cooling system 10 with a 10,000 toncapacity as described above utilizing three thermal storage units 36(e.g., 42 ft diameter, 30 ft height) and radiators may have a foot printof approximately 28,179 ft², which is approximately 24 percent smaller.Combinations of one or more of the disclosed embodiments may also beused. The various tank and piping configurations may be combined and maybe desirable to meet the requirements of particular applications.

The cooling fluid 33 referenced in the embodiments described above mayinclude primarily water. In some embodiments, the cooling fluid 33 mayinclude water with a biocide and/or corrosion inhibitors. Propylene orethylene glycol or other antifreeze can also be added to provide freezeprotection. Non-aqueous liquids, slurries, etc. are also options for thecooling fluid 33. In some embodiments with stratified thermal storageunits 36 having water-based solutions of cooling fluid 33, an additivethat reduces the temperature of minimum density of the cooling fluid 33may be utilized where the temperature of the cooling fluid 33 may bebelow approximately 39° F.

With regard to the piping forming the loops and flow paths discussedabove, in freezing climates without antifreeze, exposed piping should beinsulated and heat-traced to prevent possible freezing damage. Thethermal storage units 36 may be open and may be naturally resistant tofreezing damage, although heaters or insulation may be desirable in somecases.

It should be noted that certain embodiments described here can also beused as a heat pump for heating applications. A distinction betweenemploying present embodiments as a heating system rather that cooling isthat heat leaving the condenser is considered the primary output,although the system can simultaneously provide cooling as a usefuloutput. A variation for heat pumps is to cool refrigerant liquid usingincoming ventilation air either directly or through a secondary (glycol)loop.

While only certain features and embodiments have been illustrated anddescribed, many modifications and changes may occur to those skilled inthe art (e.g., variations in sizes, dimensions, structures, shapes andproportions of the various elements, values of parameters (e.g.,temperatures, pressures, etc.), mounting arrangements, use of materials,colors, orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited in the claims.The order or sequence of any process or method steps may be varied orre-sequenced according to alternative embodiments. It is, therefore, tobe understood that the appended claims are intended to cover all suchmodifications and changes as fall within the true spirit of theinvention. Furthermore, in an effort to provide a concise description ofthe exemplary embodiments, all features of an actual implementation maynot have been described (i.e., those unrelated to the presentlycontemplated best mode of carrying out the invention, or those unrelatedto enabling the claimed invention). It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation specific decisions may be made.Such a development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure, without undue experimentation.

The invention claimed is:
 1. A system, comprising: a refrigerant circuitconfigured to flow a refrigerant, comprising: a compressor in therefrigerant circuit; a condenser in the refrigerant circuit; anexpansion device configured to expand the refrigerant in the refrigerantcircuit; a subcooling heat exchanger disposed between the condenser andthe expansion device in the refrigerant circuit; and a cooling heatexchanger in the refrigerant circuit, wherein the refrigerant flowingthrough the cooling heat exchanger is configured to cool a load fluidflowing through the cooling heat exchanger in a subcooling mode; achilled fluid pump coupled to the cooling heat exchanger, wherein thechilled fluid pump is configured to pump the load fluid from a load tothe cooling heat exchanger in the subcooling mode; and a subcoolingcircuit configured to flow a cooling fluid, comprising: the subcoolingheat exchanger in the subcooling circuit, wherein the cooling fluid isconfigured to cool the refrigerant in the subcooling heat exchanger inthe subcooling mode; a subcooling pump in the subcooling circuit,wherein the subcooling pump is configured to pump the cooling fluid froma thermal storage unit to the subcooling heat exchanger in thesubcooling mode; and the thermal storage unit configured to store thecooling fluid in the subcooling circuit; wherein the thermal storageunit is fluidly coupled to the cooling heat exchanger in a rechargemode, the load is isolated from the cooling heat exchanger in therecharge mode, the subcooling pump is turned off in the recharge mode,the chilled fluid pump is configured to pump the cooling fluid from thethermal storage unit to the cooling heat exchanger in the recharge mode,and the thermal storage unit receives the cooling fluid from the coolingheat exchanger after the cooling fluid is cooled by the refrigerant inthe cooling heat exchanger in the recharge mode.
 2. The system of claim1, wherein the thermal storage unit comprises a stratified cooling fluidtank.
 3. The system of claim 1, wherein the thermal storage unitcomprises a cooling fluid tank comprising a moveable partition defininga first reservoir and a second reservoir of the cooling fluid tank. 4.The system of claim 3, wherein the moveable partition comprises: aninsulation layer; a weight coupled to the insulation layer; and a linercoupled to the insulation layer and the cooling fluid tank, wherein theliner forms a watertight seal between the first reservoir and the secondreservoir.
 5. The system of claim 1, wherein a flow rate of the coolingfluid is such that an increase in temperature of the cooling fluidacross the subcooling heat exchanger is approximately equal to adecrease in temperature of the refrigerant across the subcooling heatexchanger.
 6. The system of claim 1, wherein an effectiveness of thesubcooling heat exchanger is greater than approximately 90 percent. 7.The system of claim 1, wherein the subcooling heat exchanger comprises amulti-pass brazed-plate heat exchanger that approximates counterflowbetween the refrigerant and the cooling fluid.
 8. The system of claim 1,wherein the thermal storage unit comprises a subterranean ground loop.9. The system of claim 1, wherein the thermal storage unit comprises: afirst tank configured to supply a cold cooling fluid to the subcoolingpump; a second tank configured to receive a warm cooling fluid from thesubcooling heat exchanger; and a third tank fluidly coupled to the firsttank and to the second tank, wherein the third tank is configured tocool warm cooling fluid received from the second tank into the coldcooling fluid, to provide the cold cooling fluid to the first tank, andto thermally isolate the cold cooling fluid in the first tank from thewarm cooling fluid in the second tank.
 10. The system of claim 1,wherein the cooling heat exchanger is configured to cool a chilled waterflow with the refrigerant, and the chilled water flow is supplied to acooling load.
 11. The system of claim 1, wherein the subcooling pump iscoupled to a bottom of the thermal storage unit, wherein in thesubcooling mode, the subcooling pump is configured to flow the coolingfluid to the subcooling heat exchanger from the bottom of the thermalstorage unit, through the subcooling heat exchanger, and to a top of thethermal storage unit.
 12. The system of claim 1, wherein during therecharge mode the chilled fluid pump is configured to pump the coolingfluid through the cooling heat exchanger at a tank pressure of thethermal storage unit, and during the subcooling mode the chilled fluidpump is configured to pump the load fluid through the cooling heatexchanger at a load pressure different than the tank pressure.